1. Field of the Invention
The present invention relates to intermittent gas flow units useful for providing intermittent flow of gas, which units are useful in any environment wherein an intermittent flow of gas is desired, for example, with membrane separation units to provide cleaning of the membrane separation units. The present invention also relates to membrane separation units, such as membrane separation units including a plurality of membrane modules, such as hollow fiber membrane modules. The present invention also relates to filtering and separating liquid in a treatment tank by performing suction through membranes, such as through hollow fiber membranes submerged in the liquid in the treatment tank.
2. Discussion of Background Information
When food wastewater, sewage, or sludge, is decomposed, for example, a large amount of aeration is required in a treatment tank, so that bacteria can breath in the treatment tank. Since a direct impact of aeration for bacteria may damage hollow fiber membranes, the hollow fiber membranes are protected from aeration. Meanwhile, the liquid in the treatment tank is pumped through hollow fiber membranes, and thereby liquid that has permeated the membranes is filtered and separated, and obtained as filtered and treated water. Since suspended matters deposited on an external side of the hollow fiber membranes reduce filtration performance, an appropriate amount of aeration is provided to the external side of the hollow fiber membranes, so as to remove the suspended matters deposited on the external side of the hollow fiber membranes.
A submerged membrane apparatus is disclosed in Japanese Patent Laid-Open Publication No. H7-185270, the disclosure of which is incorporated by reference herein in its entirety, having a membrane unit submerged in liquid in a treatment tank and providing filtered and treated water that has permeated the membrane. The submerged membrane apparatus is provided with an aerator generating coarse bubbles and an aerator generating fine bubbles below the membrane unit in the treatment tank.
When continuous aeration is performed, however, electricity expenses are incurred to constantly supply air, and life of hollow fiber membranes is shortened due to damage from being continuously aerated. Although Japanese Patent Laid-Open Publication No. H7-185270 does not describe specific intermittent operations of the aerators, a separate control system is generally required to control intermittent operation. Such a separate control system leads to disadvantages, including a complex structure and cost increase. For example, intermittent supply of air controlled by valves includes the use of large pipes and high pump costs with the valves being hard to maintain.
Accordingly, there is a need in the art for intermittent supply of gas that includes a simple device that is capable of providing a high volume of gas, preferably in the form of bubbles, preferably from a continuous flow of gas.